Multimedia streams that are sought to be protected (e.g., pay-per-view sporting events, movies, and the like) can be encrypted at the transmitter (colloquially referred to as the “head end”) with keys in a way that receiving television set-top boxes (STBs) that have complementary keys can decrypt the content for viewing. Accordingly, cable service providers must use head end conditional access (CA) devices that encrypt multimedia streams in accordance with the capabilities of the set-top boxes of the viewers. Many of these capabilities, including decryption capabilities, are proprietary to the makers of the set-top boxes.
It happens that only a very few “incumbent” companies sell most of the set-top boxes. Accordingly, competitors seeking to enter the cable television set-top box market must license the proprietary keys from the incumbents, often at high prices. This reduces competition.
A straightforward alternative way to permit competitive STB makers to enter the market without paying licensing fees to the incumbents would be to encourage the cable service providers, at their head ends, to completely encrypt each stream with as many CA devices (using respective sets of keys) as there are set-top box providers. This, however, would plainly undesirably multiply the amount of bandwidth necessary to carry a program. Accordingly, Sony has developed an encryption scheme whereby only “critical” portions, such as I-frames or headers, of a stream are encrypted, with the remainder of the stream being sent in the clear but being useless without being able to decrypt the “critical” portions. In this way, only the critical portions need be duplicated in encrypted form, not the entire stream. With more specificity, only the critical portions are encrypted both by the existing (“legacy”) CA devices using the incumbents' keys and by a secondary conditional access process using a competitor's keys. Published U.S. patent application Ser. No. 10/038,217, filed Jan. 2, 2002 and incorporated herein by reference, discloses such a scheme.
As understood herein, the legacy CA components that are made by the incumbent providers can be programmed by the incumbent providers to detect that the above-mentioned process is ongoing. Consequently, the legacy components might be programmed by the incumbents to defeat the process and, thus, to maintain a de facto monopoly. Having recognized this possibility, the solution below is provided.